In general, a hermetic compressor is employed in a cooling cycle of a refrigerator or an air conditioner to compress a refrigerant and includes a compression unit for compressing the refrigerant and a motor for providing a compression driving force of the refrigerant. The hermetic compressor including the compression unit and the motor is accommodated in a hermetic case.
The compression unit may include a piston that compresses the refrigerant through the linear reciprocation movement. In addition, the motor generally includes a stator and a rotor rotated through the electromagnetic interaction with the stator as current is applied to the stator.
A frame is installed in the hermetic case to install the compression unit and the motor thereon. Typically, the rotor is rotatably supported by a journal bearing installed at an inner upper portion of the frame, and the stator is fixed to an upper outer portion of the frame while surrounding the rotor.
The driving force of the motor is transferred to the compression unit through a rotation shaft. One end of the rotation shaft is press-fitted into the center of the rotor to rotate together with the rotor and the other end of the rotation shaft extends to the lower portion of the frame while rotatably passing through the journal bearing.
An eccentric shaft is provided at an end of the rotation shaft extending to the lower portion of the frame such that the eccentric shaft is eccentrically rotated as the rotation shaft is rotated, and a connecting rod is installed between the eccentric shaft and the piston in order to convert the eccentric rotational movement of the eccentric shaft into the linear reciprocation movement of the piston. Thus, the driving force of the motor is transferred to the compression unit through the rotation shaft.
However, the conventional hermetic compressor has the following problems.
That is, in the conventional hermetic compressor, in which the rotor is provided in the stator, a diameter of the rotor that rotates together with the rotation shaft is smaller than that of the stator, so the rotor may not generate high torque.
In addition, in the conventional hermetic compressor, in which the size of the stator provided outside the rotor is larger than the size of the rotor, the amount of coils wound around the stator is increased, so it is not economic in terms of the usage of materials.
Therefore, recently, there have been attempts to provide a hermetic compressor employing a motor, in which a rotor is installed outside a stator to increase a diameter of the rotor and to reduce the amount of coils wound around the stator.